Figure 3.

Substitutions in the Q_p site affect CII activity less severely in the native environment. (a) Oxygen consumption of digitonin-permeabilized cells respiring on 10 mM succinate in the presence of rotenone and ADP (coupled) and the maximal rate after addition of FCCP (uncoupled). While I56F and S68A variants support the respiration on succinate, B9 and R72C cells are deficient. The S68A defect is apparent only upon uncoupling. Mean±S.E.M. of 3–4 independent experiments. The symbol * indicates values significantly different from WT in the coupled state (oneway ANOVA), the symbol # values significantly different from WT in the uncoupled state (oneway ANOVA) and the symbol ** values significantly increased after FCCP addition (t-test). (b) Intracellular succinate measured by mass spectroscopy in extracts from an equal number of cells indicates functional CII in the WT, I56F and S68A. Mean±S.E.M. of two independent experiments, the symbol * indicates values significantly different from WT